Phosphorus
Fertilizer Can Be Effective For Many Years

Phosphorus fertilizer, while
expensive, is often necessary for wheat, barley, corn and other crops to
produce profitable yields. Now Agricultural
Research Service research has shown that phosphorus does not have to be
applied annually to get good yields.

ARS soil scientist Ardell D. Halvorson, of the agency's
Soil, Plant and Nutrient Research
Laboratory in Fort Collins, Colo., conducted several long-term experiments
in the Great Plains on farm fields in Montana, Colorado and Nebraska. In
Montana, he found that a single application of phosphorus increased soil test
levels and crop yields for more than 17 years. His research in Nebraska and
Colorado also showed that farmers can expect improved yields for several years
after a single phosphorus treatment.

Since phosphorus is expensive, many farmers tend to use less than the ideal
amount each year. Through his research, Halvorson has found economic returns to
be greater when applying the correct amount of phosphorus the first year, to
eliminate phosphorus deficiency, and then skipping two or three years. Initial
cost will be higher, but farmers are likely to have greater profits in the long
term.

Halvorson recommends applying higher, adequate rates of phosphorus
initially, then lower rates as needed to maintain optimum crop yields. Since
cropping intensity influences how quickly phosphorus is used, farmers may have
to apply it more often if using annual cropping systems, rather than
wheat/fallow. But they still don't have to apply it every year.

If a farmer is only renting the land for a short period of time, the
investment for an initial large application of phosphorus may not make sense.
However, for landowners, applying the optimal amount every few years will
likely produce larger yields.

Since neither soil nor phosphorus leaches readily under Great Plains
conditions, the only way a farmer can really "lose" it is through
soil erosion, runoff and crop removal.